The present disclosure relates to methods for cleaning extrusion dies such as those used in forming inorganic materials.
Extrusion dies are used in processes for extrusion-forming materials into bodies or articles of a given extrusion-forming material (“batch material”). Extrusion dies may contain passages or channels of relatively minute cross-sectional area, which extend through the dies, and through which the batch material passes. After the end of a production run the extrusion dies are generally cleaned and inspected. If the batch material is not removed from the extrusion passage and channels, the batch material can harden and become set in the die, thereby damaging the die and/or resulting in poor quality of the extruded form. Additionally, extrusion dies may require cleaning prior to changing the batch material or upon shutting down the extruder to avoid damage to the dies. Examples of extrusion dies are disclosed in U.S. Pat. No. 6,803,087, which is incorporated herein by reference.
In the past, dies for making ceramic honeycombs for diesel and automotive substrates were cleaned with high-pressure water washers (such as, for example, those having approximately 1000-3000 psi nozzle pressure). While water washers had been used successfully for several years to remove the ceramic batch, the water pressure washers had to be run for long cycles to achieve adequate cleaning of the dies. Some cycles took several hours, which may not be acceptable in certain manufacturing environments where the turn-around time on the die wash may affect production.
A wax press method was then developed to clean extrusion dies. In that method, wax “cookies” were pressed into a batch material filled die, thereby purging the batch material from the slots and holes of the die. The wax remaining in the die was then melted from the die leaving the die free of batch material. While the wax press method quickly removed the batch material from the die, it had several disadvantages. For example, the wax was expensive, the wax left a greasy residue on the die, and melting the residual wax from the die was time consuming. Additionally, the wax required costly and time consuming environmental disposal.
Moreover, in the wax press method, to completely clean the wax from the die, another step of cleaning was required using solvents such as hexane or methylene chloride, which are flammable and/or toxic. The wax residue could also be removed by heating the die to 600° C. to burn the wax off the die; however, such high temperatures can damage the die. Complete removal of the wax is particularly important nevertheless. For example, the die must be completely clean for instances of reapplication of chemical vapor deposition (“CVD”) wear resistant coatings on the die.
U.S. Pat. No. 3,084,075, incorporated herein by reference, discloses, inter alia, a method for cleaning dough-extruding dies comprising pressing or extruding a solid waxy material through a die to remove dough residue, and then removing the residual wax using water heated to a temperature above the melting point of the wax.
The wax press method was eventually abandoned and replaced, again with high-pressure water washers which are currently in use for cleaning extrusion dies, such as diesel and automotive thin-wall honeycomb dies, for example. As stated above, while water washers have been used successfully for several years, as die technology improves thereby allowing for thinner slots and holes, and as dies become thicker in order to produce larger diameter honeycombs, the water washers must be run for even longer cycles to achieve adequate cleaning of the dies. Some cycles can take several hours, which may not be acceptable in certain manufacturing environments where the turn-around time on the die wash may affect production. Moreover, the high pressure of the washer may cause bending of the die pins or other damage to the die.
U.S. Pat. No. 7,040,327, incorporated herein by reference, discloses, inter alia, a variation on the high-pressure water washing method that first heats the die to 200-500° C. to burn out the organic binder in the ceramic and then places the die in a high-pressure washing cycle. While this variation potentially speeds the washing cycle, the overall cycle of die cleaning remains slow as the die first has to be heated and held for a sufficient time, for example 4-24 hours, to burn out the organic binder. In addition, some ceramic pastes when heated to those temperatures can set up in the die (like cement) and become even more difficult or impossible to remove from the die.
The inventors have now discovered time and cost-effective methods for cleaning dies that are, in various embodiments, capable of cleaning the dies without damaging them. According to various embodiments, the present disclosure relates to methods for cleaning extrusion dies, such as those used in forming inorganic materials.
Although the present invention may obviate one or more of the above-mentioned disadvantages, it should be understood that some aspects of the invention might not necessarily obviate one or more of those disadvantages.